Olefinic polymers such as polyethylene, polypropylene, polyvinyl chloride, polystyrene and polyesters are subject to photooxidation when exposed to sunlight over extended periods of time. This photo-oxidation initiates deterioration of the polymer by breaking the polymer chain and by causing formation of carbonyl groups in the molecule. As the oxidation continues, the polyolefin cracks or crazes and loses tensile strength to the point of mechanical failure. A number of ultraviolet inhibitors have been proposed which inhibit photo-degradation of many polymers, resins and polyesters. However, some of the most effective of these known ultraviolet inhibitors, such as lower alkyl hydroxyphenyl benzotriazoles, are not compatible with such polyolefins as polyethylene, polyropylene and polystyrene and polymers which contain high molecular weight hydrocarbon chains due to exudation from the polymer soon after being incorporated therein.
Also it has been found that many effective stabilizers for halogen-containing polymers such as polyvinyl chloride, polyvinylidene chloride and the like are not effective stabilizers for hydrocarbon polyolefins, since stabilizers for such halogen-containing polymers function essentially as halide scavengers, thus serving no purpose in the hydrocarbon olefinic polymers and which, in some cases, actually alter desirable properties of the hydrocarbon polymer. similarly, certain stabilizers which are emminently suitable as UV inhibitors in such cellulose ester polymers as cellulose triacetate and cellulose acetate butyrate are not sufficiently effective for hydrocarbon polymers.
Although certain benzotriazole stabilizers have been recently proposed in U.S. Pat. Nos. 3,230,194 and 3,253,921, these benzotriazoles are normally solid substances which are mixed with the polymer to provide protection but which are not retained over long duration in the polymeric material and, therefore, do not provide lasting protection against UV light absorption. It is believed that these benzotriazoles in their normally solid state do not penetrate the internal polymeric structure for lasting incorporation therein. Similar difficulties are encountered with triazoles containing polar substituents such as SO.sub.2 NH.sub.2, amine derivatives thereof, SO.sub.3 Na, COONa, etc. Additionally, in the case of the lower alkyl benzotriazoles, the lower alkyl substituents are known to be incompatible with high molecular weight hydrocarbon type polymers, as is the case with stabilizers proposed in U.S. Pat. No. 3,018,269. In other cases, crowding of the alkyl substituent vicinal to the --OH group on the phenol ring produced a hindered phenol moiety which alters the UV absorption range, so that compounds such as 2-(3'-alkyl-2'-hydroxyphenyl)benzotriazoles and the 2-hydroxyphenyl naphthotriazoles are not sufficiently sensitive to effectively prevent deterioration due to UV light radiations within the critical 2,900 to 3,700A band range which most often causes the degradation of the polymer through discoloration and crazing.
In the case of non-polymeric materials, it is known that certain dyes are not resistant to the effects of sunlight and fade when exposed to ultraviolet radiation within the range of 250-400mu. Many transparent materials useful in sheets or films, in addition to developing undesirable color resulting in the reduction of transparency, also become brittle, lose their elasticity, crack and eventually completely deteriorate. Paints, varnishes, lacquers, and the like are particularly prone to these effects, and in connection with these latter materials, the transparency factor is of paramount concern. Thus, it is of prime importance that any stabilizer employed for these purposes be colorless and chemically inert so as to avoid coloration or formation of colored impurities.
It is therefore an object of this invention to provide an ultraviolet absorbent and heat stabilization material of the benzotriazole type capable of conferring a high degree of long lasting stability to the olefinic and other polymers and non-polymeric materials, which stabilizer is substantially colorless and which is obtained in a state capable of intimate and uniform penetration into the internal polymeric structure or molecular arrangement of non-polymeric materials.
Another object of this invention is to provide a stabilizer which displays optimum absorption activity for utraviolet radiations within the range of 250 to 400 mu which functions as a complete sun-screen when employed in relatively high concentration.
It is another object of this invention to provide a method for preparing such an improved stabilizer of the benzotriazole type.
It is a further object of this invention to provide novel polymeric compositions containing a completely compatible stabilizer which provides sustained protection to the polymer and displays high tolerance for other additives in the polymeric formulation.
It is also an object of this invention to provide a stabilizer of the benzotriazole type which is highly soluble in a wide variety of solvents and which, therefore, is suitable for intimate incorporation in many substances including polymeric and non-polymeric materials.
It is still another object to provide a stabilizer of high efficiency and long duration for most polymeric materials, including halogen, oxygen and nitrogen containing polymers and for paints, dyes, varnishes and cosmetic substances.
Still another object is to obtain a stabilizing composition which is capable of providing sustained protection against deterioration by UV light radiation which is not readily exuded from a formulation or removed by mechanical abrasion.
These and other objects of the present invention will become apparent from the following description and disclosure.
According to the present invention, a normally liquid composition for stabilizing heat and light sensitive materials, comprising essentially a normally liquid mixture of branched chain dodecyl isomers of 2-(5'-dodecyl-2'-hydroxyphenyl)benzotriazole is provided together with a method for preparing said liquid mixture and for preparing products, particularly plastic, paint or dye products, having incorporated therein between about 0.01% and about 15% by weight preferably between 0.05 and 10% by weight of said normally liquid mixture.
The 2-(5'-dodecyl-2'-hydroxyphenyl)benzotriazole isomeric mixtures which comprise the normally liquid stabilizers of the present invention consist essentially of secondary and tertiary dodecyl isomers substituted in the para position with respect to the hydroxy group of the phenol moiety. For the purposes of the present invention, the isomeric mixture generally contains at least 4 dodecyl isomers, preferably a mixture of 6 to 12 isomeric forms, wherein the predominant proportion of the dodecyl isomers contain a preponderance of carbon atoms in the alkyl carbon chain on which branching occurs, most preferably at least about 70% of dodecyl isomers having at least 7 carbon atoms in an alkyl carbon chain. The n-dodecyl isomer is substantially eliminated from the present mixture by a selective manner in which the liquid mixture is prepared. However, when the present mixture of isomers is prepared by alternative methods, as in direct formulation of two or more certain selected branched chain types, trace amounts of the n-dodecyl isomer may be tolerated in the formulation. If desired, however, this isomer can be completely removed by extraction.
The preferred method of preparing the instant normally liquid stabilizers comprising the 2-(5'-dodecyl-2'-hydroxyphenyl) benzotriazole isomeric mixtures involves coupling an o-nitrophenyl diazonium salt, obtained from the reaction of a 2-nitroaniline with an alkali metal nitrite in the presence of a mineral acid, with a mixture of branched chain dodecyl isomers of 4-dodecylphenyl in the presence of a carboxylic acid, eg. glacial acetic acid or an alkali salt of the carboxylic acid, in an acid medium maintained at a pH of between about 3 and about 5.5, preferably at a pH between 3.5 and 4.5.
The o-nitrophenyl diazonium salt employed in the coupling reaction is obtained by reacting 2-nitroaniline, eg. at a temperature between about -7.degree.C and about 10.degree.C under substantially atmospheric pressure, with an equimolar amount or an excess of alkali metal nitrite in the presence of a strong non-oxidizing and non-reducing mineral acid such as a hydrogen halide, sulfuric acid, phosphoric acid, etc.; hydrochloric and sulfuric acids being preferred.
The nitroaniline reactant is dissolved in a suitable solvent. For example, a solution of the nitroaniline is formed by mixture with a carboxylic C.sub.2 to C.sub.4 acid, eg. glacial acetic acid, and the mineral acid is added to the solution to form a slurry. The resulting slurry of 2-nitroaniline is then reacted with the nitrite in the presence of a strong mineral acid referred to above. Suitable alkali metal nitrites include the nitrites of any of the alkali or alkaline earth metals and are preferably the sodium or potassium nitrites. Any excess nitrite which may remain after completion of the reaction can be neutralized with a suitable neutralizer eg. sulfamic acid.
The isomeric mixture of branched chain 4-dodecylphenol is desirably formed by polymerization of propylene to tetramer, for example, at a temperature within the range of about 50.degree. and about 100.degree.C under a pressure of 1 atmosphere to 20 atmospheres in the presence of a polymerization catalyst, such as boron trifluoride or a catalyst such as a slurry comprising aluminum alkyl, activated titanium trichloride and an alkane diluent or a boric acid-oxalic acid mixture or any of the polymerization catalysts reported on page 665 Table 3 of Catalysis by S. Berkman, J. C. Morrell and G. Egloff (1940). This polymerization provides a mixture of essentially branched chain isomers of dodecene including isotactic isomers. It is to be understood, however, that any known method of obtaining propylene tetramer in a plurality of isomeric, branched chain forms, such as by thermal or catalytic cracking of higher molecular weight polypropylene, polyethylene or other aliphatic hydrocarbon polymers and recovering the dodecyl branched chain isomers is included within the scope of this invention. This branched chain isomeric mixture is then reacted with phenol at a temperature between -15.degree.C and 75.degree.C at a pressure from 0 to 100 psig. for a period of from about 0.5 to about 2.5 hours preferably in the presence of a catalyst, eg. 0.5 to 2% of boron trifluoride catalyst, to provide a solution containing the corresponding branched chain mixture of 4-dodecylphenol isomers used in the present selective method of preparation. The product is essentially (more than 90%) p-dodecylphenol branched chain isomers. The 4-dodecyl isomers are recovered from the solution, eg. by washing with water to remove catalyst and distilling to remove any unreacted phenol.
It is also to be understood, however, that specific isomers including, for example, the 2,4,6,8-tetramethyloctyl isomer, may be selected and either added to the above isomeric mixture or may be independently combined to provide the present isomeric mixture of branched chain dodecyl isomers which are reacted with phenol as described above.
In the present method of preparation, the above coupling reaction results in the formation of the branched chain 2-(2'-nitrophenylazo)-4-dodecyl phenols. The coupling reaction is effected in the presence of a C.sub.2 to C.sub.5 carboxylic acid or an alkali metal salt of a C.sub.2 to C.sub.5 carboxylic acid, preferably a sodium or potassium salt of acetic or propionic acid, at a temperature below 30.degree.C, preferably between about -15.degree.C and about 10.degree.C and advantageously under conditions of agitation for several hours, eg. 2 to 50 hours, to form the corresponding dodecyl isomeric mixture of 2-(2'-nitrophenylazo)-4-dodecylphenols obtained as an oily liquid phase over an aqueous phase containing water, acid and salts. The oily phase is separated by decantation or by any other convenient method, and can be additionally washed with water, if desired. It is then diluted with between about 70 and 130 parts by weight preferably 90 to 110 parts by weight of a suitable solvent such as any of those hereinafter described for the present stabilizer, or mixtures thereof; most preferably benzene, xylene or toluene in admixtures with lower alcohols, after which the organic components of the oily phase are reacted with zinc under constant agitation at a temperature between about 10.degree. and about 60.degree.C or reflux in the presence of an inorganic hydroxide, such as NaOH or KOH.
In the above cyclization reaction, the mixture of aromatic solvent, (eg. benzene), alcohol, (eg. methanol or ethanol) and an alkali such as an inorganic hydroxide, (eg. KOH or NaOH) is particularly suited to provide good conversion without cleavage of the azo compound so that the zinc reactant successfully removes oxygen and effects ring closure to a triazole ring. In this reaction, a three phase system is formed comprising the zinc catalyst phase, an alcohol-benzene phase containing the triazoles and a water-inorganic hydroxide phase. The phase containing the triazole is treated with hydrogen halide to form an organic phase and an aqueous phase and the resulting organic phase water washed and then distilled under vacuum to remove solvents and other contaminants.
The purification of the crude isomeric mixture prepared by the process outlined above, which does not involve the selection and combination of certain substantially pure branched-chain isomers, is particularly important in certain cases since the crude mixture contains color forming impurities which would limit the use of the present stabilizer to applications where substantial discoloration is not an important factor.
Accordingly, the crude liquid mixture containing the triazole mixture obtained above is purified by treatment at a temperature in the range of from 20.degree.to about 150.degree.C with between about 5 and about 30 mole percent, preferably 10 to 20 mole percent, of an organic anhydride selected from the group consisting of alkyl anhydrides containing from 3 to 8 carbon atoms, such as propionic anhydride, acetic anhydride, acetic formic anhydride and aromatic anhydrides of 8 to 12 carbon atoms such as phthalic anhydride and succinic anhydride. The preferred anhydrides, however, are acetic and propionic anhydride. This treatment with the organic anhydride is usually conducted over a period of from about 0.5 to 5 hours and is effected preferably at a temperature between about 30.degree.C and about 100.degree.C at atmospheric or slightly superatmospheric pressure. The anhydride converts undesirable color forming impurities, for example, aminophenol by-products which impart a black or dark brown coloration to non-distillable amides so that, in the subsequent distillation conducted under vacuum, these impurities remain in the distilland and are not recovered overhead in the 180.degree. to 250.degree.C boiling distillate fraction containing product. The anhydride treated mixture is then vacuum distilled, eg. under a pressure of between 0.01mm and 0.15mm Hg, preferably between 0.02 and 0.06 mm Hg.
The distillate fraction is preferably further treated by contact with air, oxygen or oxygen enriched air, for example, an air and ozone mixture, most preferably for a period of from 0.5 to 25 hours, at a temperature between about 50.degree. and about 150.degree.C, most desirably between about 70.degree. and about 120.degree.C, to convert any remaining color forming impurities, for example, phenolquinone byproducts which impart a yellow coloration and any remaining aminophenols to non-distillable polymers or other non-distillable compounds. The mixture is then redistilled and a distillate fraction boiling above Hg 180.degree.C, at 0.01-0.15mm Hg, preferably between about 185.degree. and 230.degree.C at 0.05mm Hg pressure is collected, condensed and recovered as the desired liquid mixture of branched chain dodecyl isomers of 2-(5'-dodecyl-2'-hydroxyphenyl)benzotriazole which is the product stabilizer of the present invention.
In the above preparation the pH of the coupling step is an important process condition and can be maintained by a mixture of acids such as a mixture of organic acid with an alkali salt, eg. a potassium or sodium salt of the organic acid, preferably an excess of glacial acetic with a minor proportion of sodium acetate.
The above method of operation is specific to the present stabilizers since the application of other methods to the preparation of the isomeric dodecyl stabilizer mixture, as exemplified by U.S. Pat. No. 3,230,194, resulted in a dark resinous mass which could not be purified to a useful product as for the stabilization of plastics in plastic applications. Specifically, the dodecyl phenol mixtures of the present process do not provide the desired coupling conversion when used in the process of U.S. Pat. No. 3,230,194 as is achieved in the present non-aqueous coupling reaction.
The isomeric liquid mixtures prepared by the process outlined above, have melting points below 0.degree.C and boiling points within the range of 190.degree.to 260.degree.C at 0.03 mm to 0.06 mm Hg pressure, depending upon the components of the mixture. Because of the boiling range and the normally liquid state of the present isomeric mixture which is generally of an oily consistency, the present stabilizers afford better penetration of polymeric or non-polymeric material over extended temperature ranges and periods of retention. Also, the substantially long branched chain dodecyl substituents provide better compatibility with high molecular weight hydrocarbon polymers and non-polymeric materials, and the composition comprising a mixture of the dodecyl isomers has greater solubility in polyolefins than any of the individual components of the mixture or the n-dodecyl isomer alone.
The substantially increased solubility of the present isomeric mixture over the individual solubilities of the individual components is indeed unexpected and may be explained by the interaction and association of the various isomeric components in the composition; these molecules are not sufficiently similar to allow for the formation of crystals and, hence, the present isomeric mixtures are not solids.
Surprisingly, applicant has also discovered that excessive branching, such as is present in the hexamethyl hexyl substituent, is undesirable when present in a major proportion in the isomeric mixture for the reason that the molecular shape or thickness of such dodecyl substituents seems to prevent easy entry into the intersticies of the polymeric material. As a result, such excessively branched dodecyl hydroxyphenyl benzotraizoles are usually absorbed only on the surface of the polymer and are subject to exudation from the surface sites of the polymer and removal by surface abrasion in a relatively short period of time; eg. a few months.
Additionally, it is known that normally solid stabilizers do not provide extremely good light fastness because the solid is much more susceptible to fading than a liquid. This property is of prime importance in the stabilization of dyes, paints or pigments. Since the benzotriazoles of the prior art are normally solid compounds, having melting points in the range of about 70.degree. to about 110.degree.C, coatings of these materials are readily decomposed by strong light; whereas a normally liquid, generally oily coating of the present stabilizer components is extremely resistant to high intensity light.
The mixture of isomers in the composition of the present stabilizers is responsible for maintaining the liquid state and for providing a UV absorption range which peaks at between 280 mu and 340 mu and which is particularly effective over the range of 260mu-370 mu for maximum protection as a complete sun screen. The positioning of the dodecyl substituents para to the --OH group is also important in providing an unhindered phenol moiety which possesses a higher efficiency against heat deterioration. The present isomeric mixtures possess advantages over other alkyl hydroxyphenyl benzotriazoles which disclose efficiencies in the border areas of the 200 mu or 400 mu range and which are useful for only a limited number of polymers.
The polymeric materials stabilized by the present isomeric liquid mixtures include homopolymers and copolymers of hydrocarbon olefins such as ethylene, propylene, butylene and styrene, homopolymers and copolymers of olefin halides such as vinylchloride, vinylidine chloride, and 2,3,-dichloro-1,3-butadiene, and homopolymers and copolymers of esters such as vinyl acetate, methyl methacrylate, etc. and cellulose and carbonate polymers. Terpolymers of any of the above monomers are also suitable for stabilization with the present isomeric liquid mixture. The present stabilizers are utilized in a concentration within the range of between about 0.05 and 15 weight percent preferably between about 0.1 and about 10 weight percent, most preferably between about 0.5 and about 5 weight percent based on the polymer. The liquid mixture of isomers can be incorporated by spraying on a particulate or powdered dry polymer or by adding the stabilizer to a suspension of polymer in a low molecular weight alcohol or other dispersant.
They can also be most intimately incorporated in the polymer by adding the stabilizer to the reaction during the polymerization or before curing the polymer or by immersion of the polymer in a solution of the stabilizer after polymerization is complete followed by evaporation of stabilizer solvent. Frequently, such incorporations by immersion can be effected at room temperature which is greatly advantageous in the stabilization of certain dyes and other materials which do not possess high thermal stability.
These methods of incorporating the present stabilizers in the polymeric composition are generally carried out under conventional temperature and pressure conditions which are within the range of between about 130.degree. and about 250.degree.C under atmospheric to 50 psig. pressure, preferably between about 175.degree. and about 210.degree.C at atmospheric pressure. In certain circumstances, when the stabilizer is added to a polymerization reaction mixture or before compounding and curing the polymer, the temperature and pressure extant in the system may be employed. Actually, the operable limits of conditions for addition of stabilizer may be widely varied because of the normally liquid state of the present isomeric mixture. Thus, it is possible to employ temperatures between about -30.degree. and 200.degree.C under atmospheric pressure and even higher temperatures under superatmospheric pressure, when desired.
The liquid isomeric mixture may additionally contain antioxidant, for example, a sterically hindered phenol such as 2,6-ditertiarybutyl-4-methylphenol (Ionol); dilaurylthiopropionate; distearylthiodipropionate; etc. or any other useful antioxidant. Alternatively, the present liquid isomeric mixture can be incorporated into a final polymeric formulation including the antioxidant and other additives. When employed, between about 0.1 weight percent and about 5, weight percent, more usually 0.25 to 1.5 weight percent, of antioxidant based on oxidizable species has been found suitable.
The present stabilizers are highly effective for providing stability in olefinic polymers used in making transparent sheets or films employed as a sun screen or barrier against water evaporation; in vinyl halide polymers employed as siding or roofing materials or as floor tile; in preventing yellowing of polystyrene sheets or molded forms used in lighting fixtures and in many other applications involving the use of butylene acetate, cellulose ester and acrylate polymers.
The present stabilizers may also be employed to prevent deterioration due to discoloration and oxidation in non-polymeric materials, used as commercial dyes including azo or azoic dyes, anthraquinone dyes, carbazole dyes, sulfur-containing dyes, indigoid dyes and their intermediates and ionized dye derivatives. These stabilizers provide similar protection in lacquers, paints and varnishes. Specifically "chalking" of body finishes in automobiles and other items subjected to constant exposure to the elements can be greatly reduced. Because of its high solubility in varnishes, for example, soybean alkyd varnish, the present stabilizers can be incorporated in concentrations as high as 10 to 15% to provide an exceptionally resistant finish.
For cosmetic uses, the liquid isomeric mixture can be employed in the absence or presence of a non-irritating antioxidant such as Ionol. Suitable for stabilization with the present isomeric mixtures are cosmetic preparations including cosmetic creams to prevent color degradation and promote shelf life. Use in hair dyes, conditioners or hair sprays or cosmetic ointments is particularly attractive since the present stabilizers act as barriers to completely screen out the harmful effects of the sun. In such applications, stabilizer concentrations of from 0.01 up to 15%, preferably 1 to 10% may be used. These and many other applications of the present stabilizers will become apparent from consideration of the solubility characteristics of the present liquid isomeric mixtures.
Solvents suitable for the present stabilizers include low and high boiling water immiscible organic solvents and low boiling water soluble organic solvents and dispersants. Examples of these include lower alcohols example ethanol, methanol, propanol, etc., lacquer, vehicles; oils, for example, white petrolatum, paraffin oil, linseed oil, castor oil, oil of rose, mineral or vegetable oils, olive oil, glycerin, vaseline, cocoa butter, lanolin, light petroleum oils or lubricating oils; aromatic solvents, for example, benzene, toluene or xylene; higher alcohols; resorcinol; ketones; alkyl pyrrolidones; cycloaliphatic hydrocarbons for example cyclohexane; pyrogallic acid; fatty esters; water based emulsions alkoxy alkyl acetates; ethyl- and butyl-cellusols; ethylene glycol; terpentine; bisphenols; hydroxy biphenols; triphenyl phosphate and other organic phosphates; sterically hindered phenols; for example, Ionol; phthalates for example, benzylphthalate and dibutylphthalate, ethers, for example Cellosolve, Solox and many others.
The liquid state of the present liquid isomeric mixtures allows intimate dispersion throughout the material to be stabilized without the use of solents. However, from the standpoint of economics and as a means of extending the distribution of stabilizers, a solvent or dispersant is most frequently employed. When used, the solvent or dispersant may comprise up to 80% by weight or more of the isomeric mixture.
Generally, the stabilizer is incorporated in the non-polymeric material in a manner similar to that outlined above except for obvious modifications in procedure. For example, in place of stabilizer addition to the polymer or polymerizing species, the stabilizer can be added to the carrier vehicle or may be added to a dye, dye intermediate or cosmetic formulation .